Wednesday, October 29, 2008

The Council on Tall Buildings and Urban Habitat (CTBUH) has published comments on the NIST WTC 7 Report. The CTBUH questions critical points of the NIST WTC 7 collapse theory and also highlights problems with the writing NIST report itself.

The CTBUH criticisms focus on two technical issues The conjectured failure of shear studs and bolts on the supposedly critical Column 79:

Several conclusions drawn in the NIST report on the contribution of structuralcomponents in failure initiation are unexpected and have raised concernswithin the Council. These conclusions involve the role of both shear studs andlocal global buckling of the floor beams in failure initiation. The Councilbelieves that the local connection performance was a significant part of theglobal failure and would like to have seen a more explicit analysis of theconnection failure. (See also comment on Chapters 11-13.)

The NIST analysis (p. 353), shows that shear studs and the bolts holding theprimary Column 79 failed before the temperature of the steel reached 200˚C.This implies a fundamental weakness that would be picked up by aconventional PBD analysis. These temperatures are very low compared to afire protection test that assumes that steel loses strength at 550˚C.

The failure of shear studs is surprising, and has been modeled in a verysimplistic way, which may overestimate the failure of this element. Priorstudies and real fire cases have not previously identified shear stud failure asa significant possibility Page 5

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It is difficult to understand why the top bolts of the girder would fail atconnection to Column 79 Page 5

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The report does not describe the detail failure mechanism of the girderconnection to Column 79. Since this was critical to the failure we wouldexpect to see diagrams of it, in its deflected, deformed shape immediatelyprior to collapse. Page 7

And NIST’s assertion that column buckling proceeded floor collapse:

We strongly believe that the initiating event was thefailure of the floor and the girder connections to the main column and that thisshould be documented in Section 14.3.4. Page 7

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The Council does not agree with the NIST statement that the failure was aresult of the buckling of Column 79. We believe that the failure was a result ofthe collapse of the floor structure that led to loss of lateral restraint and thenbuckling of internal columns. Page 10

However, the CTBUH also casts serious doubt on NIST’s entire thermal expansion fairy tale by suggesting that cooling was in fact taking place around the magical Column 79 at the time of failure:

It appears that the fire on Level 12 had passed its peak in the area of Column79. Is it possible that failure occurred as part of the cooling cycle? Page 6

And questions NIST’s hypothesis about floor beams buckling both theoretically and with experimental data:

It is surprising to see in-plane buckling of the beam as being a key generationof the initial failure, since it would be expected that the floors would bend outof the way on their major axis, combined with a local buckling of the bottomflange, like those found in the Cardington Fire Tests. Page 6

Finally, the CTBUH states that it finds the NIST report confusing and contradictory:

The report is rather confusing because the floor analysis is considered inSections 8, 11 and 12. It would be better if there was a completereconciliation of the analysis models. Page 6

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In these sections NIST states that the initial failure was caused by the failureof the floor system, in particular the connections to Column 79, that led to thecolumn becoming excessively slender and buckling. These statementscontradict the summary section 14.3.4 that identifies the initiating event as thebuckling of Column 79. Page 7

But don’t expect the CTBUH to come out and endorse 9/11 Truth either:

The Council would like to make it clear that it sees no credibility whatsoever inthe 911 ‘truth movement’ and we believe, with the vast majority of tall buildingprofessionals, that all the failures at the WTC (WTC 1, 2, 5, 6 and 7) were adirect or indirect result of the planes that were flown into the two towers. Wehave carefully looked at the evidence that the 911 ‘truth movement’ presentsand we cannot see any credible scientific evidence of a controlled demolitionon WTC 7 or any of the other WTC buildings. The Council considers that the‘truth movement’ is a distraction and should not obfuscate the performanceissues which should be at the center of the debate about how best to continueto improve and develop fire and life safety in tall buildings. Page 4

So, on the one hand the CTBUH provides at least three good reasons to dismiss the NIST report as a blatant fraud: (a) phenomenal shear-stud and bolt failure at Column 79, (b) cooling around Column 79 at the supposed time of thermal expansive failure and (c) mystical floor beam buckling. But on the other hand, the CTBUH ignores the blatant evidence of controlled demolition in WTC 7 for no technical reason what-so-ever.

(I do not include the CTBUH’s insistence that floor failure proceeds column failure as a reason to disregard NIST because the idea that either could cause any kind of a collapse that could be confused with a controlled demolition is plainly absurd).

It should be note the CTBUH chairman and lead author of its NIST WTC 7 Comments, David Scott, has some interesting conflicts of interest (as apparently do his co-authors):

He was in New York on 9-11, 2001 and witnessed the attack on the World Trade Center and was part of the SEAoNY engineering team that worked at Ground Zero to assist with the search, recovery and clean-up.

Following 9-11 he was extensively involved in the industry review of design standards and procedures for tall buildings in extreme events. He has authored papers on Fire Induced Progressive Collapse, and was a reviewer of the US Governments (GSA) design requirements to mitigate progressive collapse, that were issues in 2002. He also worked extensively with Daniel Libeskind on the WTC masterplan and his design for Freedom Tower.